The present invention relates to a method and a device for determining the amount of a liquid, e.g., ink for use in a printer existing in a container.
A printer, for example, includes an ink storing section storing ink for printing images. Japanese Patent Laid-Open Publication No. 8-216371, for example, discloses a device for determining the amount of ink remaining in the ink storing section. In the device disclosed in this document, the ink storing section is partly or entirely implemented as bellows or similar compressible member. A sensor is provided for sensing the position of the ink storing section and implemented by, e.g., a position sensor responsive to the position of the end of the compressible ink storing section. A pressing section is located outside of the ink storing section for pressing its end and thereby compressing the ink.
The above prior art device provides the ink storing section with a hermetic integral configuration in order to prevent the ink from drying and to promote easy refilling of the ink storing section. However, the pressing section for pressing the ink storing section has a complicated structure and needs an exclusive space therefor.
Japanese Patent Laid-Open Publication No. 10-76674, for example, teaches an ink sensing device as a solution to the above problem The ink sensing device includes a pulse signal generating section for generating a pulse signal, A differentiating circuit differentiates the pulse signal and feeds the resulting voltage signal to electrodes disposed in an ink storing section. A gate passes only the positive voltage of the voltage signal applied to the electrodes on the basis of the pulse signal output from the pulse signal generating section An ink level sensing section determine, based on the output of the gate, whether or not the ink level in the in storing section is above a preselected level. The differentiating circuit is constituted by a capacitor, a resistor and the above electrodes. The ink level sensing section is made up of a peak hold circuit and a comparator for comparing the output of the peak hold circuit and a preselected voltage.
So long as a sufficient amount of ink is available in the ink storing section, positive and negative voltages appear at the junction between the electrode and the gate when the ink storing section runs out of ink, the impedance between the electrodes varies with the result that only positive voltages lower than the peak value of the above voltages appears at the junction. On the other hand, the gate opens only when the pulse signal output from the pulse generating section is positive, so that only positive voltages are applied to the peak hold circuit. Consequently, the peak hold circuit can be driven only by a positive power source and does not need a negative power source. The comparator compares peaks held by the peak hold circuit with the preselected voltage while sending the results of comparison to a CPU (Central Processing Unit).
A problem with the above ink sensing device is that the ink contacting the electrodes deposits on the electrodes and degrades the sensing ability of the device and causes the electrodes to corrode. Another problem is that the electrodes are sealed in a cartridge formed of vinyl chloride or similar resin together with the ink and must therefore be led out to the outside of the cartridge. This makes it difficult to hermetically seal the cartridge and thereby renders the structure sophisticated. Further, electric contacts expected to contact such electrodes must be provided on the printer side, further sophisticating the structure.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Utility Model Publication No. 3-28 342 and Japanese Patent Laid-Open Publication Nos. 53-131 068, 82-146632, 5-229 243, 8-56 180, 6-155 885, 10-337 944, and 11-101 680.
It is therefore an object of the present invention to provide a method and a device capable of surely detecting the decrease of a liquid stored in a container below a preselected amount with a simple and space-saving structure and without causing electrodes to corrode.
It is another object of the present invention to provide a device for determining the amount of a liquid existing in a container and capable of producing an alarm when the liquid decreases below a preselected amount or automatically stopping the operation of an apparatus using the liquid when the container is about to run out of the liquid.
A method of determining the amount of a liquid existing in a container of the present invention has the steps of arranging a resonance circuit on the container storing the liquid, applying a voltage having a preselected frequency to a drive coil located outside of the container to thereby induce a voltage having a preselected frequency in the resonance circuit, inducing, based on the voltage induced in the resonance circuit, a voltage having a preselected frequency in a sense coil located outside of the container, and measuring the voltage induced in the sense coil.
Also, a device for determining the amount of a liquid existing in a container of the present invention includes a resonance circuit arranged on the container storing the liquid, and a drive coil and a sense coil located outside of the container. The resonance circuit includes a pair of electrodes arranged on one or both of the side and bottom of the container, a first coil connected to one of the electrodes and facing the drive coil, and a second coil connected to the other electrode and facing the sense coil.